The Drag[en]gine is a fully customizable game engine and game development environment designed with modularity and extensibility in mind not requiring expensive licenses.
One of the two rigs used on the stairs. This one here affects all AI including the player looking for logic flow in the map. All objects looking for tight fitting collision ignores this rig. Multiple such rigs would be possible for different AI for example (like one for player and one for NPCs for example).